The optimum handling and navigation of a sailing craft or other vessel requires certain frequently-updated information. Some of this information is readily obtained from instrumentation of a type commonly found on sailing craft such as a heading sensor (compass), velocity sensing equipment capable of determining both the speed of the boat in the forward direction and the speed of the boat at 90 degrees to its heading (leeway), and sensors for determining the apparent wind direction and speed. However, in normal use these five measurable parameters require mental interpolation by the operator of the boat, and such interpolation requires a high degree of judgment and experience. The exercise of such judgment has been helped in the prior art by various applications of analog and digital computing techniques which determine for the operator certain data relating to navigation which would permit the operator to know more precisely what he is doing from a quantitative point of view.
For example Taylor et al. U.S. Pat. No. 3,934,129 provides indications of average apparent wind direction and average boat speed using integrating techniques and a suitable computer. This patent also computes relative wind speed. Taylor et al. U.S. Pat. No. 3,881,094 uses a somewhat different technique for determining average boat speed and average apparent wind speed and direction, taking samples over discrete intervals of time, integrating the samples, and dropping the oldest of the samples during each sampling period. In U.S. Pat. No. 3,968,684 to Haffner, there is a further improvement resultinhg from measurements of leeway and using them to improve the determination of actual motion of the boat over the bottom.
U.S. Pat. No. 3,961,166 to Stobart is of interest in that it resolves increments of vehicle motion into distances traveled along two normal axes, and then combines these distances by taking the square root of the sum of the squares.
U.S. Pat. No. 3,875,388 to Luten et al. uses the idea of multiplexing information such as apparent wind speed and direction and hull speed into a computer which provides an output indication of the performance of the boat, the system also receiving additional information such as compass course and wave effects.
Efforts have also been made to provide an indication of actual progress toward a selected destination mark. In Polsky U.S. Pat. No. 4,107,988, an analog system of computation is used to determine progress made in an effort to hold a predetermined course toward a mark. In Chisolm et al. U.S. Pat. No. 3,821,523, there is a set of thumb switches used to set the coordinates of a destination mark into a computer. When this has been done distance signals are exchanged with a plurality of ground based DME stations and the measured distances are used to compute progress toward the coordinates set into the computer manually.
However, the prior art systems designed for use on sailing craft have generally provided only a few of the outputs which would be necessary to achieve truly optimum navigation of the boat, and these readouts are generally not consolidated and presented to the observer in such a manner as to provide quick answers without requiring an excessive amount of attention or constant manual intervention by the operator so that his attention is drawn away from his other duties at the helm in derogation thereof.
Moreover, the raw data which is directly measurable on moving craft, including its compass heading, hull speed and leeway, and apparent wind speed and direction, is not itself the final readout needed for optimum navigation. Because of the motion of the boat such readouts cannot be directly measured by instrumentation. For example, the movement of the vessel greatly changes both apparent speed and direction of the wind. The computation of vectors required for indicating actual movement of the boat over the bottom, and actual wind direction and velocity, are fairly complex and would be quite burdensome to the operator of the vessel using a pocket calculator. Moreover, vectors determined using a pocket calculator would be so few in number, and so far apart in time, as to make it practically impossible to produce accurate averaging. Averaging is of course highly desirable since it is almost impossible to hold a constant course or speed in a small sailing boat since boat heading and wind velocity are constantly changing. In addition, parameters such as leeway are continuously varying, since they depend not only upon the physical configuration of the particular boat hull, but also upon said trim and relative wind direction and velocity. Leeway can be rather a large factor, sometimes introducing a course error which can amount to twenty degrees with respect to the apparent compass heading. Mental estimates of leeway drift are difficult at best, and always inaccurate. The same is true of efforts to estimate the actual course and progress made good by the vessel over the bottom. Estimates infrequently made provide very sparse data. Thus, it is necessary to achieve averaging of a large number of calculations made at a high rate in order to determine with any degree of accuracy the actual progress of the vessel toward a predetermined destination mark.